Occupant protection apparatus of this kind include an air bag device for deploying an air bag between a steering wheel and an occupant, an impact-energy-absorption-type steering column, and a combination of the air bag device and the impact-energy-absorption-type steering column. Another occupant protection apparatus includes an air bag device incorporated in a steering wheel and an actuator for moving forward a steering column with appropriate timing in accordance with a forward movement of a driver during a vehicle collision event so as to lessen a load that is imposed on the driver when the driver interferes with the air bag incorporated in the steering wheel (Japanese Patent No. 2596200).
Conventionally, an energy absorption load; i.e., a load to be imposed on an occupant, is set such that the impact energy of the occupant can be absorbed in relation to a working stroke for energy absorption. However, when the working stroke for energy absorption cannot be set long because of restrictions on the mounting space of the vehicle, the energy absorption load is set higher as compared with the case where the working stroke can be set long. Therefore, when collision conditions and the occupant's physique are taken into consideration, the energy absorption load becomes excessively high; thus, from the viewpoint of the quantity of energy absorption by an air bag device and an impact-energy-absorption-type steering column, the working stroke may be unnecessarily long and thus fails to be effectively exploited (when the impact energy of an occupant is small, such an insufficient exploitation of the working stroke arises). Further, setting the energy absorption load to an increased level means that the load imposed on an occupant becomes high. If energy can be absorbed while the occupant is supported with load of a slightly lower level, impact energy can be effectively absorbed while the occupant is subjected to a gentler load.